1. Field of the Invention
The present invention relates to an imaging apparatus comprising an optical magnification changing mechanism which optically changes a magnification of an image and an electronic magnification changing mechanism which reduces or expands a magnification with respect to image data by signal processing.
2. Description of the Related Art
In a video camera or a digital camera having a zoom lens system, a zoom ratio is changed by moving a zoom lens, whereby a focal distance is changed to a telephoto side or a wide-angle side while a focal position is kept constant, thereby changing an object distance. However, in configuring a small imaging element, optical zooming from the wide-angle side to the telephoto side changes not continuously but in a stepwise manner when a design is made such that a group number of lenses is decreased or when a design is made such that the number of actuators is reduced.
For example, let us consider an optical system having a two-group configuration in which a first group of lenses 301 is negative and a second group of lenses 302 is positive, as shown in FIG. 18, only the second group of lenses 302 at an image side being movable. In the case where a position of the movable lens 302 has been moved as indicated by an arrow 304 as illustrated, an image surface 303 changes in a curved shape as illustrated.
That is, in the case where, in a lens of such a type as shown in FIG. 18, an optical system has been designed such that a telephoto image is formed on an image surface at a certain zoom magnification (focal distance) A, there are only a maximum of two zoom magnifications including A such that the telephoto image is formed on the image surface. Similarly, there are only a maximum of two zoom magnifications such that an image is focused at a predetermined focal distance. However, since the number of lenses can be reduced and a drive section can be simplified, there is an advantage that stepwise zooming can be configured at a small size and at a low cost.
In addition, FIG. 19A shows a cam ring mechanism which is used to simplify a drive section of an optical zoom lens. FIG. 19B is an exploded schematic view of a cam ring provided at an interior wall of a mirror frame 1013 shown in FIG. 19A. In this case, a magnification changing lens 1011 and a focusing lens 1012 are driven in accordance with cam grooves 1013a and 1013b by rotation of the mirror frame 1013. In the illustrated example, there are three steps of stepwise zooming. In this case, since one cam ring can drive two groups of lenses, it is possible to reduce the number of actuators for driving. This technique contributes to downsizing of the imaging apparatus, as in the configuration shown in FIG. 18.
Although the above-described technique can contribute downsizing of the imaging apparatus by reducing the group number of lenses or simplifying a structure of the drive section, the number of steps of optical zooming is reduced due to its structure. As a result, there is a disadvantage that a user cannot obtain a desired configuration.
On the other hand, Jpn. Pat. Appln. KOKAI Publication No. 6-339083 discloses that magnifications of a two-focus optical system and an optical finder with a zoom are made coincident with each other by using a magnification changing process using an electron zoom (electronic magnification change). In addition, Jpn. Pat. Appln. KOKAI Publication No. 2003-283910 discloses that, in order to substantially match angles of view of an optical finder and imaging system while a drive control system of the optical finder and a stepwise zooming imaging lens is used in common, the stepwise zooming at a magnification, which does not exceed a magnification of the optical finder but is proximal thereto, is selected when the magnification is specified, and adjustment of an angle of view is carried out by electronic zooming. In Jpn. Pat. Appln. KOKAI Publication No. 2001-136436, a magnification changing process is carried out by using a technique of optical/electronic magnification change for canceling a fluctuation of an angel of view due to a change of a photography mode (still picture or motion picture).
On the other hand, in recent years, a video camera has incorporated an electronic zooming function for electronically changing an image magnification by using an imaging element other than such optical zooming. The electronic zooming function is a function of changing a focal distance to the telephoto side without moving a zoom lens so as to convert an imaging signal of size which is smaller than a light receiving screen size of the imaging element to a video signal which corresponds to the light receiving screen size. In a video camera having such an electronic zooming function, an imaging signal of size which is greater than the light receiving screen size of the imaging element cannot be obtained. For this reason, zooming to the wide-angle side has not be successfully achieved although zooming to the telephoto side can be achieved.
In contrast, there is proposed an apparatus and a method for substantially generating an image at the wide-angle side while fixing a lens by utilizing a difference between the number of pixels of the imaging element and the number of pixels of an output image. An imaging apparatus enabling such electronic zooming includes an imaging apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2000-295530, for example. This publication discloses a solid state imaging apparatus having photoelectric conversion pixels arranged two-dimensionally, for randomly providing an access to the photoelectric conversion pixels, the apparatus comprising first skipping means for reading out an arbitrarily specified pixel and second skipping means for reading out an image region which is smaller than an image frame read out by the first skipping means, wherein the number of pixels read out by the first and second skipping means are made equal to each other.
Further, Jpn. Pat. Appln. KOKAI Publication No. 10-42183 discloses an imaging apparatus comprising: first adjusting means for optically changing an angle of view of an image; a second adjusting means for electrically changing an angle of view of an image; and control means for controlling the first adjusting means and the second adjusting means to determine an angle of view, wherein the control means has been configured to adjust an angle of view to a desired angle of view by the second adjusting means and substantially move the control of the angle of view from the second adjusting means to the first adjusting means while maintaining the angle of view. Specifically, the imaging apparatus disclosed in this publication uses a CCD type imaging element. When electronic zooming is carried out, all pixels are read out from the CCD type imaging element, and the read-out pixels are temporarily stored in a frame memory or the like. Then, an electrical interpolating process is carried out on the basis of a pixel signal relating to a small number of pixels included in a partial area of a full angle of view.
Jpn. Pat. Appln. KOKAI Publication No. 6-339083 discloses that magnifications of a two-focus optical system and an optical finder with a zoom are coincided with each other by using a magnification changing process with electronic zooming. Moreover, Jpn. Pat. Appln. KOKAI Publication No. 2002-314868 discloses an imaging apparatus using an imaging element which is capable of specifying a readout position and range on the imaging element by reading out a photoelectric conversion signal on the imaging element in accordance with an X-Y address system, and further, carrying out thinning-out readout based on the same number of clocks. There is disclosed that the imaging apparatus makes control by using electronic zooming means for carrying out electronic zooming for changing an isolation angle of view which is obtained as an isolation range of an imaging position and an imaging angle of view; and the electronic zooming and optical zooming in combination, whereby a zooming range of an output angle of view associated with a finally output image signal is controlled so as to be substantially wider than any of an optical zoom range which can be produced by only a change of the imaging angle of view and an electronic zoom range which can be produced by only a change of the isolation angle of view.
In addition, Japanese Patent Application No. 2002-249968 proposes a method of reducing distortion of an image obtained during readout with respect to distortion of an image caused by thinning-out readout by using spatial and temporal interpolation, and obtaining a high quality image, wherein a step width of the thinning-out readout can be finely produced to a certain degree.